/*
 * Platform-independent bits of X11 forwarding.
 */

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <time.h>

#include "putty.h"
#include "ssh.h"
#include "tree234.h"

#define GET_16BIT(endian, cp)                                                  \
  (endian == 'B' ? GET_16BIT_MSB_FIRST(cp) : GET_16BIT_LSB_FIRST(cp))

#define PUT_16BIT(endian, cp, val)                                             \
  (endian == 'B' ? PUT_16BIT_MSB_FIRST(cp, val) : PUT_16BIT_LSB_FIRST(cp, val))

const char *const x11_authnames[] = {
    "", "MIT-MAGIC-COOKIE-1", "XDM-AUTHORIZATION-1"};

struct XDMSeen {
  unsigned int time;
  unsigned char clientid[6];
};

struct X11Connection {
  const struct plug_function_table *fn;
  /* the above variable absolutely *must* be the first in this structure */
  unsigned char firstpkt[12]; /* first X data packet */
  tree234 *authtree;
  struct X11Display *disp;
  char *auth_protocol;
  unsigned char *auth_data;
  int data_read, auth_plen, auth_psize, auth_dlen, auth_dsize;
  int verified;
  int throttled, throttle_override;
  int no_data_sent_to_x_client;
  char *peer_addr;
  int peer_port;
  struct ssh_channel *c; /* channel structure held by ssh.c */
  Socket s;
};

static int xdmseen_cmp(void *a, void *b)
{
  struct XDMSeen *sa = a, *sb = b;
  return sa->time > sb->time
             ? 1
             : sa->time < sb->time
                   ? -1
                   : memcmp(sa->clientid, sb->clientid, sizeof(sa->clientid));
}

/* Do-nothing "plug" implementation, used by x11_setup_display() when it
 * creates a trial connection (and then immediately closes it).
 * XXX: bit out of place here, could in principle live in a platform-
 *      independent network.c or something */
static void dummy_plug_log(Plug p,
                           int type,
                           SockAddr addr,
                           int port,
                           const char *error_msg,
                           int error_code)
{
}
static void dummy_plug_closing(Plug p,
                               const char *error_msg,
                               int error_code,
                               int calling_back)
{
}
static void dummy_plug_receive(Plug p, int urgent, char *data, int len)
{
}
static void dummy_plug_sent(Plug p, int bufsize)
{
}
static int dummy_plug_accepting(Plug p,
                                accept_fn_t constructor,
                                accept_ctx_t ctx)
{
  return 1;
}
static const struct plug_function_table dummy_plug = {dummy_plug_log,
                                                      dummy_plug_closing,
                                                      dummy_plug_receive,
                                                      dummy_plug_sent,
                                                      dummy_plug_accepting};

struct X11FakeAuth *x11_invent_fake_auth(tree234 *authtree, int authtype)
{
  struct X11FakeAuth *auth = snew(struct X11FakeAuth);
  int i;

  /*
   * This function has the job of inventing a set of X11 fake auth
   * data, and adding it to 'authtree'. We must preserve the
   * property that for any given actual authorisation attempt, _at
   * most one_ thing in the tree can possibly match it.
   *
   * For MIT-MAGIC-COOKIE-1, that's not too difficult: the match
   * criterion is simply that the entire cookie is correct, so we
   * just have to make sure we don't make up two cookies the same.
   * (Vanishingly unlikely, but we check anyway to be sure, and go
   * round again inventing a new cookie if add234 tells us the one
   * we thought of is already in use.)
   *
   * For XDM-AUTHORIZATION-1, it's a little more fiddly. The setup
   * with XA1 is that half the cookie is used as a DES key with
   * which to CBC-encrypt an assortment of stuff. Happily, the stuff
   * encrypted _begins_ with the other half of the cookie, and the
   * IV is always zero, which means that any valid XA1 authorisation
   * attempt for a given cookie must begin with the same cipher
   * block, consisting of the DES ECB encryption of the first half
   * of the cookie using the second half as a key. So we compute
   * that cipher block here and now, and use it as the sorting key
   * for distinguishing XA1 entries in the tree.
   */

  if (authtype == X11_MIT) {
    auth->proto = X11_MIT;

    /* MIT-MAGIC-COOKIE-1. Cookie size is 128 bits (16 bytes). */
    auth->datalen = 16;
    auth->data = snewn(auth->datalen, unsigned char);
    auth->xa1_firstblock = NULL;

    while (1) {
      for (i = 0; i < auth->datalen; i++)
        auth->data[i] = random_byte();
      if (add234(authtree, auth) == auth)
        break;
    }

    auth->xdmseen = NULL;
  } else {
    assert(authtype == X11_XDM);
    auth->proto = X11_XDM;

    /* XDM-AUTHORIZATION-1. Cookie size is 16 bytes; byte 8 is zero. */
    auth->datalen = 16;
    auth->data = snewn(auth->datalen, unsigned char);
    auth->xa1_firstblock = snewn(8, unsigned char);
    memset(auth->xa1_firstblock, 0, 8);

    while (1) {
      for (i = 0; i < auth->datalen; i++)
        auth->data[i] = (i == 8 ? 0 : random_byte());
      memcpy(auth->xa1_firstblock, auth->data, 8);
      des_encrypt_xdmauth(auth->data + 9, auth->xa1_firstblock, 8);
      if (add234(authtree, auth) == auth)
        break;
    }

    auth->xdmseen = newtree234(xdmseen_cmp);
  }
  auth->protoname = dupstr(x11_authnames[auth->proto]);
  auth->datastring = snewn(auth->datalen * 2 + 1, char);
  for (i = 0; i < auth->datalen; i++)
    sprintf(auth->datastring + i * 2, "%02x", auth->data[i]);

  auth->disp = NULL;
  auth->share_cs = auth->share_chan = NULL;

  return auth;
}

void x11_free_fake_auth(struct X11FakeAuth *auth)
{
  if (auth->data)
    smemclr(auth->data, auth->datalen);
  sfree(auth->data);
  sfree(auth->protoname);
  sfree(auth->datastring);
  sfree(auth->xa1_firstblock);
  if (auth->xdmseen != NULL) {
    struct XDMSeen *seen;
    while ((seen = delpos234(auth->xdmseen, 0)) != NULL)
      sfree(seen);
    freetree234(auth->xdmseen);
  }
  sfree(auth);
}

int x11_authcmp(void *av, void *bv)
{
  struct X11FakeAuth *a = (struct X11FakeAuth *)av;
  struct X11FakeAuth *b = (struct X11FakeAuth *)bv;

  if (a->proto < b->proto)
    return -1;
  else if (a->proto > b->proto)
    return +1;

  if (a->proto == X11_MIT) {
    if (a->datalen < b->datalen)
      return -1;
    else if (a->datalen > b->datalen)
      return +1;

    return memcmp(a->data, b->data, a->datalen);
  } else {
    assert(a->proto == X11_XDM);

    return memcmp(a->xa1_firstblock, b->xa1_firstblock, 8);
  }
}

struct X11Display *x11_setup_display(const char *display, Conf *conf)
{
  struct X11Display *disp = snew(struct X11Display);
  char *localcopy;

  if (!display || !*display) {
    localcopy = platform_get_x_display();
    if (!localcopy || !*localcopy) {
      sfree(localcopy);
      localcopy = dupstr(":0"); /* plausible default for any platform */
    }
  } else
    localcopy = dupstr(display);

  /*
   * Parse the display name.
   *
   * We expect this to have one of the following forms:
   *
   *  - the standard X format which looks like
   *    [ [ protocol '/' ] host ] ':' displaynumber [ '.' screennumber ]
   *    (X11 also permits a double colon to indicate DECnet, but
   *    that's not our problem, thankfully!)
   *
   * 	- only seen in the wild on MacOS (so far): a pathname to a
   * 	  Unix-domain socket, which will typically and confusingly
   * 	  end in ":0", and which I'm currently distinguishing from
   * 	  the standard scheme by noting that it starts with '/'.
   */
  if (localcopy[0] == '/') {
    disp->unixsocketpath = localcopy;
    disp->unixdomain = TRUE;
    disp->hostname = NULL;
    disp->displaynum = -1;
    disp->screennum = 0;
    disp->addr = NULL;
  } else {
    char *colon, *dot, *slash;
    char *protocol, *hostname;

    colon = host_strrchr(localcopy, ':');
    if (!colon) {
      sfree(disp);
      sfree(localcopy);
      return NULL; /* FIXME: report a specific error? */
    }

    *colon++ = '\0';
    dot = strchr(colon, '.');
    if (dot)
      *dot++ = '\0';

    disp->displaynum = atoi(colon);
    if (dot)
      disp->screennum = atoi(dot);
    else
      disp->screennum = 0;

    protocol = NULL;
    hostname = localcopy;
    if (colon > localcopy) {
      slash = strchr(localcopy, '/');
      if (slash) {
        *slash++ = '\0';
        protocol = localcopy;
        hostname = slash;
      }
    }

    disp->hostname = *hostname ? dupstr(hostname) : NULL;

    if (protocol)
      disp->unixdomain =
          (!strcmp(protocol, "local") || !strcmp(protocol, "unix"));
    else if (!*hostname || !strcmp(hostname, "unix"))
      disp->unixdomain = platform_uses_x11_unix_by_default;
    else
      disp->unixdomain = FALSE;

    if (!disp->hostname && !disp->unixdomain)
      disp->hostname = dupstr("localhost");

    disp->unixsocketpath = NULL;
    disp->addr = NULL;

    sfree(localcopy);
  }

  /*
   * Look up the display hostname, if we need to.
   */
  if (!disp->unixdomain) {
    const char *err;

    disp->port = 6000 + disp->displaynum;
    disp->addr = name_lookup(disp->hostname,
                             disp->port,
                             &disp->realhost,
                             conf,
                             ADDRTYPE_UNSPEC,
                             NULL,
                             NULL);

    if ((err = sk_addr_error(disp->addr)) != NULL) {
      sk_addr_free(disp->addr);
      sfree(disp->hostname);
      sfree(disp->unixsocketpath);
      sfree(disp);
      return NULL; /* FIXME: report an error */
    }
  }

  /*
   * Try upgrading an IP-style localhost display to a Unix-socket
   * display (as the standard X connection libraries do).
   */
  if (!disp->unixdomain && sk_address_is_local(disp->addr)) {
    SockAddr ux = platform_get_x11_unix_address(NULL, disp->displaynum);
    const char *err = sk_addr_error(ux);
    if (!err) {
      /* Create trial connection to see if there is a useful Unix-domain
       * socket */
      const struct plug_function_table *dummy = &dummy_plug;
      Socket s = sk_new(sk_addr_dup(ux), 0, 0, 0, 0, 0, (Plug)&dummy);
      err = sk_socket_error(s);
      sk_close(s);
    }
    if (err) {
      sk_addr_free(ux);
    } else {
      sk_addr_free(disp->addr);
      disp->unixdomain = TRUE;
      disp->addr = ux;
      /* Fill in the rest in a moment */
    }
  }

  if (disp->unixdomain) {
    if (!disp->addr)
      disp->addr =
          platform_get_x11_unix_address(disp->unixsocketpath, disp->displaynum);
    if (disp->unixsocketpath)
      disp->realhost = dupstr(disp->unixsocketpath);
    else
      disp->realhost = dupprintf("unix:%d", disp->displaynum);
    disp->port = 0;
  }

  /*
   * Fetch the local authorisation details.
   */
  disp->localauthproto = X11_NO_AUTH;
  disp->localauthdata = NULL;
  disp->localauthdatalen = 0;
  platform_get_x11_auth(disp, conf);

  return disp;
}

void x11_free_display(struct X11Display *disp)
{
  sfree(disp->hostname);
  sfree(disp->unixsocketpath);
  if (disp->localauthdata)
    smemclr(disp->localauthdata, disp->localauthdatalen);
  sfree(disp->localauthdata);
  sk_addr_free(disp->addr);
  sfree(disp);
}

#define XDM_MAXSKEW 20 * 60 /* 20 minute clock skew should be OK */

static const char *x11_verify(unsigned long peer_ip,
                              int peer_port,
                              tree234 *authtree,
                              char *proto,
                              unsigned char *data,
                              int dlen,
                              struct X11FakeAuth **auth_ret)
{
  struct X11FakeAuth match_dummy; /* for passing to find234 */
  struct X11FakeAuth *auth;

  /*
   * First, do a lookup in our tree to find the only authorisation
   * record that _might_ match.
   */
  if (!strcmp(proto, x11_authnames[X11_MIT])) {
    /*
     * Just look up the whole cookie that was presented to us,
     * which x11_authcmp will compare against the cookies we
     * currently believe in.
     */
    match_dummy.proto = X11_MIT;
    match_dummy.datalen = dlen;
    match_dummy.data = data;
  } else if (!strcmp(proto, x11_authnames[X11_XDM])) {
    /*
     * Look up the first cipher block, against the stored first
     * cipher blocks for the XDM-AUTHORIZATION-1 cookies we
     * currently know. (See comment in x11_invent_fake_auth.)
     */
    match_dummy.proto = X11_XDM;
    match_dummy.xa1_firstblock = data;
  } else {
    return "Unsupported authorisation protocol";
  }

  if ((auth = find234(authtree, &match_dummy, 0)) == NULL)
    return "Authorisation not recognised";

  /*
   * If we're using MIT-MAGIC-COOKIE-1, that was all we needed. If
   * we're doing XDM-AUTHORIZATION-1, though, we have to check the
   * rest of the auth data.
   */
  if (auth->proto == X11_XDM) {
    unsigned long t;
    time_t tim;
    int i;
    struct XDMSeen *seen, *ret;

    if (dlen != 24)
      return "XDM-AUTHORIZATION-1 data was wrong length";
    if (peer_port == -1)
      return "cannot do XDM-AUTHORIZATION-1 without remote address data";
    des_decrypt_xdmauth(auth->data + 9, data, 24);
    if (memcmp(auth->data, data, 8) != 0)
      return "XDM-AUTHORIZATION-1 data failed check"; /* cookie wrong */
    if (GET_32BIT_MSB_FIRST(data + 8) != peer_ip)
      return "XDM-AUTHORIZATION-1 data failed check"; /* IP wrong */
    if ((int)GET_16BIT_MSB_FIRST(data + 12) != peer_port)
      return "XDM-AUTHORIZATION-1 data failed check"; /* port wrong */
    t = GET_32BIT_MSB_FIRST(data + 14);
    for (i = 18; i < 24; i++)
      if (data[i] != 0) /* zero padding wrong */
        return "XDM-AUTHORIZATION-1 data failed check";
    tim = time(NULL);
    if (((unsigned long)t - (unsigned long)tim + XDM_MAXSKEW) > 2 * XDM_MAXSKEW)
      return "XDM-AUTHORIZATION-1 time stamp was too far out";
    seen = snew(struct XDMSeen);
    seen->time = t;
    memcpy(seen->clientid, data + 8, 6);
    assert(auth->xdmseen != NULL);
    ret = add234(auth->xdmseen, seen);
    if (ret != seen) {
      sfree(seen);
      return "XDM-AUTHORIZATION-1 data replayed";
    }
    /* While we're here, purge entries too old to be replayed. */
    for (;;) {
      seen = index234(auth->xdmseen, 0);
      assert(seen != NULL);
      if (t - seen->time <= XDM_MAXSKEW)
        break;
      sfree(delpos234(auth->xdmseen, 0));
    }
  }
  /* implement other protocols here if ever required */

  *auth_ret = auth;
  return NULL;
}

void x11_get_auth_from_authfile(struct X11Display *disp,
                                const char *authfilename)
{
  FILE *authfp;
  char *buf, *ptr, *str[4];
  int len[4];
  int family, protocol;
  int ideal_match = FALSE;
  char *ourhostname;

  /*
   * Normally we should look for precisely the details specified in
   * `disp'. However, there's an oddity when the display is local:
   * displays like "localhost:0" usually have their details stored
   * in a Unix-domain-socket record (even if there isn't actually a
   * real Unix-domain socket available, as with OpenSSH's proxy X11
   * server).
   *
   * This is apparently a fudge to get round the meaninglessness of
   * "localhost" in a shared-home-directory context -- xauth entries
   * for Unix-domain sockets already disambiguate this by storing
   * the *local* hostname in the conveniently-blank hostname field,
   * but IP "localhost" records couldn't do this. So, typically, an
   * IP "localhost" entry in the auth database isn't present and if
   * it were it would be ignored.
   *
   * However, we don't entirely trust that (say) Windows X servers
   * won't rely on a straight "localhost" entry, bad idea though
   * that is; so if we can't find a Unix-domain-socket entry we'll
   * fall back to an IP-based entry if we can find one.
   */
  int localhost = !disp->unixdomain && sk_address_is_local(disp->addr);

  authfp = fopen(authfilename, "rb");
  if (!authfp)
    return;

  ourhostname = get_hostname();

  /* Records in .Xauthority contain four strings of up to 64K each */
  buf = snewn(65537 * 4, char);

  while (!ideal_match) {
    int c, i, j, match = FALSE;

#define GET                                                                    \
  do {                                                                         \
    c = fgetc(authfp);                                                         \
    if (c == EOF)                                                              \
      goto done;                                                               \
    c = (unsigned char)c;                                                      \
  } while (0)
    /* Expect a big-endian 2-byte number giving address family */
    GET;
    family = c;
    GET;
    family = (family << 8) | c;
    /* Then expect four strings, each composed of a big-endian 2-byte
     * length field followed by that many bytes of data */
    ptr = buf;
    for (i = 0; i < 4; i++) {
      GET;
      len[i] = c;
      GET;
      len[i] = (len[i] << 8) | c;
      str[i] = ptr;
      for (j = 0; j < len[i]; j++) {
        GET;
        *ptr++ = c;
      }
      *ptr++ = '\0';
    }
#undef GET

    /*
     * Now we have a full X authority record in memory. See
     * whether it matches the display we're trying to
     * authenticate to.
     *
     * The details we've just read should be interpreted as
     * follows:
     *
     *  - 'family' is the network address family used to
     *    connect to the display. 0 means IPv4; 6 means IPv6;
     *    256 means Unix-domain sockets.
     *
     *  - str[0] is the network address itself. For IPv4 and
     *    IPv6, this is a string of binary data of the
     *    appropriate length (respectively 4 and 16 bytes)
     *    representing the address in big-endian format, e.g.
     *    7F 00 00 01 means IPv4 localhost. For Unix-domain
     *    sockets, this is the host name of the machine on
     *    which the Unix-domain display resides (so that an
     *    .Xauthority file on a shared file system can contain
     *    authority entries for Unix-domain displays on
     *    several machines without them clashing).
     *
     *  - str[1] is the display number. I've no idea why
     *    .Xauthority stores this as a string when it has a
     *    perfectly good integer format, but there we go.
     *
     *  - str[2] is the authorisation method, encoded as its
     *    canonical string name (i.e. "MIT-MAGIC-COOKIE-1",
     *    "XDM-AUTHORIZATION-1" or something we don't
     *    recognise).
     *
     *  - str[3] is the actual authorisation data, stored in
     *    binary form.
     */

    if (disp->displaynum < 0 || disp->displaynum != atoi(str[1]))
      continue; /* not the one */

    for (protocol = 1; protocol < lenof(x11_authnames); protocol++)
      if (!strcmp(str[2], x11_authnames[protocol]))
        break;
    if (protocol == lenof(x11_authnames))
      continue; /* don't recognise this protocol, look for another */

    switch (family) {
    case 0: /* IPv4 */
      if (!disp->unixdomain && sk_addrtype(disp->addr) == ADDRTYPE_IPV4) {
        char buf[4];
        sk_addrcopy(disp->addr, buf);
        if (len[0] == 4 && !memcmp(str[0], buf, 4)) {
          match = TRUE;
          /* If this is a "localhost" entry, note it down
           * but carry on looking for a Unix-domain entry. */
          ideal_match = !localhost;
        }
      }
      break;
    case 6: /* IPv6 */
      if (!disp->unixdomain && sk_addrtype(disp->addr) == ADDRTYPE_IPV6) {
        char buf[16];
        sk_addrcopy(disp->addr, buf);
        if (len[0] == 16 && !memcmp(str[0], buf, 16)) {
          match = TRUE;
          ideal_match = !localhost;
        }
      }
      break;
    case 256: /* Unix-domain / localhost */
      if ((disp->unixdomain || localhost) && ourhostname &&
          !strcmp(ourhostname, str[0]))
        /* A matching Unix-domain socket is always the best
         * match. */
        match = ideal_match = TRUE;
      break;
    }

    if (match) {
      /* Current best guess -- may be overridden if !ideal_match */
      disp->localauthproto = protocol;
      sfree(disp->localauthdata); /* free previous guess, if any */
      disp->localauthdata = snewn(len[3], unsigned char);
      memcpy(disp->localauthdata, str[3], len[3]);
      disp->localauthdatalen = len[3];
    }
  }

done:
  fclose(authfp);
  smemclr(buf, 65537 * 4);
  sfree(buf);
  sfree(ourhostname);
}

static void x11_log(Plug p,
                    int type,
                    SockAddr addr,
                    int port,
                    const char *error_msg,
                    int error_code)
{
  /* We have no interface to the logging module here, so we drop these. */
}

static void x11_send_init_error(struct X11Connection *conn,
                                const char *err_message);

static void x11_closing(Plug plug,
                        const char *error_msg,
                        int error_code,
                        int calling_back)
{
  struct X11Connection *xconn = (struct X11Connection *)plug;

  if (error_msg) {
    /*
     * Socket error. If we're still at the connection setup stage,
     * construct an X11 error packet passing on the problem.
     */
    if (xconn->no_data_sent_to_x_client) {
      char *err_message = dupprintf("unable to connect to forwarded "
                                    "X server: %s",
                                    error_msg);
      x11_send_init_error(xconn, err_message);
      sfree(err_message);
    }

    /*
     * Whether we did that or not, now we slam the connection
     * shut.
     */
    sshfwd_unclean_close(xconn->c, error_msg);
  } else {
    /*
     * Ordinary EOF received on socket. Send an EOF on the SSH
     * channel.
     */
    if (xconn->c)
      sshfwd_write_eof(xconn->c);
  }
}

static void x11_receive(Plug plug, int urgent, char *data, int len)
{
  struct X11Connection *xconn = (struct X11Connection *)plug;

  if (sshfwd_write(xconn->c, data, len) > 0) {
    xconn->throttled = 1;
    xconn->no_data_sent_to_x_client = FALSE;
    sk_set_frozen(xconn->s, 1);
  }
}

static void x11_sent(Plug plug, int bufsize)
{
  struct X11Connection *xconn = (struct X11Connection *)plug;

  sshfwd_unthrottle(xconn->c, bufsize);
}

/*
 * When setting up X forwarding, we should send the screen number
 * from the specified local display. This function extracts it from
 * the display string.
 */
int x11_get_screen_number(char *display)
{
  int n;

  n = host_strcspn(display, ":");
  if (!display[n])
    return 0;
  n = strcspn(display, ".");
  if (!display[n])
    return 0;
  return atoi(display + n + 1);
}

/*
 * Called to set up the X11Connection structure, though this does not
 * yet connect to an actual server.
 */
struct X11Connection *x11_init(tree234 *authtree,
                               void *c,
                               const char *peeraddr,
                               int peerport)
{
  static const struct plug_function_table fn_table = {
      x11_log, x11_closing, x11_receive, x11_sent, NULL};

  struct X11Connection *xconn;

  /*
   * Open socket.
   */
  xconn = snew(struct X11Connection);
  xconn->fn = &fn_table;
  xconn->auth_protocol = NULL;
  xconn->authtree = authtree;
  xconn->verified = 0;
  xconn->data_read = 0;
  xconn->throttled = xconn->throttle_override = 0;
  xconn->no_data_sent_to_x_client = TRUE;
  xconn->c = c;

  /*
   * We don't actually open a local socket to the X server just yet,
   * because we don't know which one it is. Instead, we'll wait
   * until we see the incoming authentication data, which may tell
   * us what display to connect to, or whether we have to divert
   * this X forwarding channel to a connection-sharing downstream
   * rather than handling it ourself.
   */
  xconn->disp = NULL;
  xconn->s = NULL;

  /*
   * Stash the peer address we were given in its original text form.
   */
  xconn->peer_addr = peeraddr ? dupstr(peeraddr) : NULL;
  xconn->peer_port = peerport;

  return xconn;
}

void x11_close(struct X11Connection *xconn)
{
  if (!xconn)
    return;

  if (xconn->auth_protocol) {
    sfree(xconn->auth_protocol);
    sfree(xconn->auth_data);
  }

  if (xconn->s)
    sk_close(xconn->s);

  sfree(xconn->peer_addr);
  sfree(xconn);
}

void x11_unthrottle(struct X11Connection *xconn)
{
  if (!xconn)
    return;

  xconn->throttled = 0;
  if (xconn->s)
    sk_set_frozen(xconn->s, xconn->throttled || xconn->throttle_override);
}

void x11_override_throttle(struct X11Connection *xconn, int enable)
{
  if (!xconn)
    return;

  xconn->throttle_override = enable;
  if (xconn->s)
    sk_set_frozen(xconn->s, xconn->throttled || xconn->throttle_override);
}

static void x11_send_init_error(struct X11Connection *xconn,
                                const char *err_message)
{
  char *full_message;
  int msglen, msgsize;
  unsigned char *reply;

  full_message = dupprintf("%s X11 proxy: %s\n", appname, err_message);

  msglen = strlen(full_message);
  reply = snewn(8 + msglen + 1 + 4, unsigned char); /* include zero */
  msgsize = (msglen + 3) & ~3;
  reply[0] = 0;                              /* failure */
  reply[1] = msglen;                         /* length of reason string */
  memcpy(reply + 2, xconn->firstpkt + 2, 4); /* major/minor proto vsn */
  PUT_16BIT(xconn->firstpkt[0], reply + 6, msgsize >> 2); /* data len */
  memset(reply + 8, 0, msgsize);
  memcpy(reply + 8, full_message, msglen);
  sshfwd_write(xconn->c, (char *)reply, 8 + msgsize);
  sshfwd_write_eof(xconn->c);
  xconn->no_data_sent_to_x_client = FALSE;
  sfree(reply);
  sfree(full_message);
}

static int x11_parse_ip(const char *addr_string, unsigned long *ip)
{

  /*
   * See if we can make sense of this string as an IPv4 address, for
   * XDM-AUTHORIZATION-1 purposes.
   */
  int i[4];
  if (addr_string &&
      4 == sscanf(addr_string, "%d.%d.%d.%d", i + 0, i + 1, i + 2, i + 3)) {
    *ip = (i[0] << 24) | (i[1] << 16) | (i[2] << 8) | i[3];
    return TRUE;
  } else {
    return FALSE;
  }
}

/*
 * Called to send data down the raw connection.
 */
int x11_send(struct X11Connection *xconn, char *data, int len)
{
  if (!xconn)
    return 0;

  /*
   * Read the first packet.
   */
  while (len > 0 && xconn->data_read < 12)
    xconn->firstpkt[xconn->data_read++] = (unsigned char)(len--, *data++);
  if (xconn->data_read < 12)
    return 0;

  /*
   * If we have not allocated the auth_protocol and auth_data
   * strings, do so now.
   */
  if (!xconn->auth_protocol) {
    xconn->auth_plen = GET_16BIT(xconn->firstpkt[0], xconn->firstpkt + 6);
    xconn->auth_dlen = GET_16BIT(xconn->firstpkt[0], xconn->firstpkt + 8);
    xconn->auth_psize = (xconn->auth_plen + 3) & ~3;
    xconn->auth_dsize = (xconn->auth_dlen + 3) & ~3;
    /* Leave room for a terminating zero, to make our lives easier. */
    xconn->auth_protocol = snewn(xconn->auth_psize + 1, char);
    xconn->auth_data = snewn(xconn->auth_dsize, unsigned char);
  }

  /*
   * Read the auth_protocol and auth_data strings.
   */
  while (len > 0 && xconn->data_read < 12 + xconn->auth_psize)
    xconn->auth_protocol[xconn->data_read++ - 12] = (len--, *data++);
  while (len > 0 &&
         xconn->data_read < 12 + xconn->auth_psize + xconn->auth_dsize)
    xconn->auth_data[xconn->data_read++ - 12 - xconn->auth_psize] =
        (unsigned char)(len--, *data++);
  if (xconn->data_read < 12 + xconn->auth_psize + xconn->auth_dsize)
    return 0;

  /*
   * If we haven't verified the authorisation, do so now.
   */
  if (!xconn->verified) {
    const char *err;
    struct X11FakeAuth *auth_matched = NULL;
    unsigned long peer_ip;
    int peer_port;
    int protomajor, protominor;
    void *greeting;
    int greeting_len;
    unsigned char *socketdata;
    int socketdatalen;
    char new_peer_addr[32];
    int new_peer_port;

    protomajor = GET_16BIT(xconn->firstpkt[0], xconn->firstpkt + 2);
    protominor = GET_16BIT(xconn->firstpkt[0], xconn->firstpkt + 4);

    assert(!xconn->s);

    xconn->auth_protocol[xconn->auth_plen] = '\0'; /* ASCIZ */

    peer_ip = 0; /* placate optimiser */
    if (x11_parse_ip(xconn->peer_addr, &peer_ip))
      peer_port = xconn->peer_port;
    else
      peer_port = -1; /* signal no peer address data available */

    err = x11_verify(peer_ip,
                     peer_port,
                     xconn->authtree,
                     xconn->auth_protocol,
                     xconn->auth_data,
                     xconn->auth_dlen,
                     &auth_matched);
    if (err) {
      x11_send_init_error(xconn, err);
      return 0;
    }
    assert(auth_matched);

    /*
     * If this auth points to a connection-sharing downstream
     * rather than an X display we know how to connect to
     * directly, pass it off to the sharing module now.
     */
    if (auth_matched->share_cs) {
      sshfwd_x11_sharing_handover(xconn->c,
                                  auth_matched->share_cs,
                                  auth_matched->share_chan,
                                  xconn->peer_addr,
                                  xconn->peer_port,
                                  xconn->firstpkt[0],
                                  protomajor,
                                  protominor,
                                  data,
                                  len);
      return 0;
    }

    /*
     * Now we know we're going to accept the connection, and what
     * X display to connect to. Actually connect to it.
     */
    sshfwd_x11_is_local(xconn->c);
    xconn->disp = auth_matched->disp;
    xconn->s = new_connection(sk_addr_dup(xconn->disp->addr),
                              xconn->disp->realhost,
                              xconn->disp->port,
                              0,
                              1,
                              0,
                              0,
                              (Plug)xconn,
                              sshfwd_get_conf(xconn->c));
    if ((err = sk_socket_error(xconn->s)) != NULL) {
      char *err_message = dupprintf("unable to connect to"
                                    " forwarded X server: %s",
                                    err);
      x11_send_init_error(xconn, err_message);
      sfree(err_message);
      return 0;
    }

    /*
     * Write a new connection header containing our replacement
     * auth data.
     */
    socketdatalen = 0; /* placate compiler warning */
    socketdata = sk_getxdmdata(xconn->s, &socketdatalen);
    if (socketdata && socketdatalen == 6) {
      sprintf(new_peer_addr,
              "%d.%d.%d.%d",
              socketdata[0],
              socketdata[1],
              socketdata[2],
              socketdata[3]);
      new_peer_port = GET_16BIT_MSB_FIRST(socketdata + 4);
    } else {
      strcpy(new_peer_addr, "0.0.0.0");
      new_peer_port = 0;
    }

    greeting = x11_make_greeting(xconn->firstpkt[0],
                                 protomajor,
                                 protominor,
                                 xconn->disp->localauthproto,
                                 xconn->disp->localauthdata,
                                 xconn->disp->localauthdatalen,
                                 new_peer_addr,
                                 new_peer_port,
                                 &greeting_len);

    sk_write(xconn->s, greeting, greeting_len);

    smemclr(greeting, greeting_len);
    sfree(greeting);

    /*
     * Now we're done.
     */
    xconn->verified = 1;
  }

  /*
   * After initialisation, just copy data simply.
   */

  return sk_write(xconn->s, data, len);
}

void x11_send_eof(struct X11Connection *xconn)
{
  if (xconn->s) {
    sk_write_eof(xconn->s);
  } else {
    /*
     * If EOF is received from the X client before we've got to
     * the point of actually connecting to an X server, then we
     * should send an EOF back to the client so that the
     * forwarded channel will be terminated.
     */
    if (xconn->c)
      sshfwd_write_eof(xconn->c);
  }
}

/*
 * Utility functions used by connection sharing to convert textual
 * representations of an X11 auth protocol name + hex cookie into our
 * usual integer protocol id and binary auth data.
 */
int x11_identify_auth_proto(const char *protoname)
{
  int protocol;

  for (protocol = 1; protocol < lenof(x11_authnames); protocol++)
    if (!strcmp(protoname, x11_authnames[protocol]))
      return protocol;
  return -1;
}

void *x11_dehexify(const char *hex, int *outlen)
{
  int len, i;
  unsigned char *ret;

  len = strlen(hex) / 2;
  ret = snewn(len, unsigned char);

  for (i = 0; i < len; i++) {
    char bytestr[3];
    unsigned val = 0;
    bytestr[0] = hex[2 * i];
    bytestr[1] = hex[2 * i + 1];
    bytestr[2] = '\0';
    sscanf(bytestr, "%x", &val);
    ret[i] = val;
  }

  *outlen = len;
  return ret;
}

/*
 * Construct an X11 greeting packet, including making up the right
 * authorisation data.
 */
void *x11_make_greeting(int endian,
                        int protomajor,
                        int protominor,
                        int auth_proto,
                        const void *auth_data,
                        int auth_len,
                        const char *peer_addr,
                        int peer_port,
                        int *outlen)
{
  unsigned char *greeting;
  unsigned char realauthdata[64];
  const char *authname;
  const unsigned char *authdata;
  int authnamelen, authnamelen_pad;
  int authdatalen, authdatalen_pad;
  int greeting_len;

  authname = x11_authnames[auth_proto];
  authnamelen = strlen(authname);
  authnamelen_pad = (authnamelen + 3) & ~3;

  if (auth_proto == X11_MIT) {
    authdata = auth_data;
    authdatalen = auth_len;
  } else if (auth_proto == X11_XDM && auth_len == 16) {
    time_t t;
    unsigned long peer_ip = 0;

    x11_parse_ip(peer_addr, &peer_ip);

    authdata = realauthdata;
    authdatalen = 24;
    memset(realauthdata, 0, authdatalen);
    memcpy(realauthdata, auth_data, 8);
    PUT_32BIT_MSB_FIRST(realauthdata + 8, peer_ip);
    PUT_16BIT_MSB_FIRST(realauthdata + 12, peer_port);
    t = time(NULL);
    PUT_32BIT_MSB_FIRST(realauthdata + 14, t);

    des_encrypt_xdmauth(
        (const unsigned char *)auth_data + 9, realauthdata, authdatalen);
  } else {
    authdata = realauthdata;
    authdatalen = 0;
  }

  authdatalen_pad = (authdatalen + 3) & ~3;
  greeting_len = 12 + authnamelen_pad + authdatalen_pad;

  greeting = snewn(greeting_len, unsigned char);
  memset(greeting, 0, greeting_len);
  greeting[0] = endian;
  PUT_16BIT(endian, greeting + 2, protomajor);
  PUT_16BIT(endian, greeting + 4, protominor);
  PUT_16BIT(endian, greeting + 6, authnamelen);
  PUT_16BIT(endian, greeting + 8, authdatalen);
  memcpy(greeting + 12, authname, authnamelen);
  memcpy(greeting + 12 + authnamelen_pad, authdata, authdatalen);

  smemclr(realauthdata, sizeof(realauthdata));

  *outlen = greeting_len;
  return greeting;
}
